Some paid sites are very US-centric: for example, Shutterstock only offer legal indemnity if you post materials to their US office; a pain for
users outside the US, yet we pay the same for the images.

The growth in popularity of stock photo sites means that the same photos turn up again and again. Only today I saw a design competition entry based around the same photo I had once used. It is a failure of stock photo sites which keep selling the same photo again and again. They don't tell you how many times it has already been sold, so they make this problem much more common than authors would like. There are many examples of the problem here.

However, all sites, free or paid, come with some risk. As many of you know, I think copyright law (and "intellectual property" law) is far too restrictive, and would favour removing many of the restrictions on re-using material that currently exist, and instead allow far more to fall within fair use. I share my work widely, allowing it to be used freely for many purposes (I'll post about an educational use in the near future). Likewise I am against DRM, and never add it to my own books. Unfortunately it is the big media organisations with money that politicians listen to.

And thus it opens the floodgates to all sorts of scams. A common one is to use a fake account to seed photos on stock photo sites (free or paid). Then when the photos are used in good faith, the scammer can send threatening letters claiming extortionate fees to avoid legal action. Even if you buy the photo from a stock site it doesn't mean you are safe - for example the basic Shutterstock licence only agrees to cover you up to $10,000 (which could be a lot less than the courts might make you pay). Oops.

Current copyright law means that even when you are sensible, you can still get caught out. Bear in mind the tips on my images page. No-one wants to face this situation. Also consider taking your own photos, which is easy and much lower risk, depending on the subject. Graphic software like Gimp makes it easy to edit images and composite them together.